#include <stdio.h>
#define N 10000
main()
  { int i, p, q, t, id[N];
    for (i = 0; i < N; i++) id[i] = i;
    while (scanf("%d %d\n", &p, &q) == 2)
      { 
        if (id[p] == id[q]) continue;
        for (t = id[p], i = 0; i < N; i++)
          if (id[i] == t) id[i] = id[q];
        printf(" %d %d\n", p, q);
      }
 }